When transmitting transmission data based on the protocol of Transmission Control Protocol (TCP)/Internet Protocol (IP), the transmission data is packetized by a transmission side device, and the packets are transmitted to a receiving side device. In Non-Patent Document 1, CUBIC is shown as an example of the congestion control algorithm that is used in order to avoid congestion when transmitting the transmission data based on the protocol of TCP/IP.
CUBIC controls the size of data that the transmission side device can transmit continuously without waiting for an acknowledgement from the receiving side device.
A transmission side device using CUBIC reduces the size of data that can be continuously transmitted without waiting for an acknowledgement when packet discard occurs. When the elapsed time from the last occurrence of packet discard is short, the size of data that can be continuously transmitted without waiting for an acknowledgement is greatly increased exponentially with respect to the elapsed time. When the size of the data that can be continuously transmitted without waiting for an acknowledgement becomes close to the saturation point, the increase in the size of data that can be continuously transmitted without waiting for an acknowledgement is set to almost zero. When more time has elapsed, the size of the data that can be continuously transmitted without waiting for an acknowledgement is slowly increased again.
That is, the transmission side device using CUBIC controls the traffic of data communication by controlling the size of data that can be continuously transmitted, thereby avoiding congestion.